Bone damage and damage to associated tissues from less severe injury can typically heal naturally. Other damage from more severe injuries to bone and related tissues caused by extreme trauma and complications associated with disease or genetic conditions, often require surgery, tissue grafts, or artificial implants in order to reconstruct these tissue in order to reestablish function or reduce associated pain. The reconstruction results from these interventions are often less than ideal. Engineered biomaterial composites can be developed to produce a biological function beyond that which naturally exists or is compromised due to injury or disease.
For example, there are 23 discs in the human spine. Discs have an outer annulus fibrosus, which surrounds an inner nucleus pulposus. The annulus fibrosus is made of several layers of fibrocartilage. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel with a consistency of jelly. The nucleus of the disc acts as a shock absorber, absorbing the impact of the body's daily activities and keeping the vertebrae separated. In certain conditions, the jelly nucleus pulposus is forced out of its natural anatomical location and may apply pressure to or induce inflammation in nerves or nerve ganglia local to the disc.
Degeneration-related and trauma-induced damage to the spinal discs are currently treated with cells, growth factors, injectable materials, such as silicone fluid or elastomer, or surgical procedures such as tissue removal in conjunction with or without spinal implants which often induce vertebral fusion. Generally, repair of damaged disc as functional living tissue is difficult. The cause of disc degeneration has been speculated to be a resultant of poor disc nutrient supply and waste removal. The inner nucleus pulposus of the disc is largely nourished and relieved of metabolites by transport through the upper and lower vertebral endplates and less so through the annulus fibrosus. Various medical conditions, such as sclerosis, damage the vertebral endplates and limit diffusion to and from the disc. This lack of transport to and from the disc likely impedes present regenerative treatment systems in the repair of damaged discs. This disease etiology is paralleled in other joints as well. Diffusion limiting changes in the calcified and vascular tissues of subchondral and cancellous bone precede the onset of osteoarthritic joint failure in diarthrodial joints as well.
Osteoarthritic degenerative joint disease and disorders of the spinal column (discs and vertebrae) accounted for an estimated 815,000 and 634,000 US diagnoses in discharged inpatients, respectively, during 2007. These occurrences were ranked fourth and ninth in prevalence, excluding pregnancy and childbirth related instances, and resulted in a financial burden of $20.2 billion (inflation-adjusted hospital costs). Levit K W, L. Stranges, E. Ryan, K Elixhauser, A, HCUP Facts and Figures: Statistics on Hospital-based Care in the United States, 2007. 2009, Agency for Healthcare Research and Quality: Rockville, Md. Degeneration is associated with an overwhelming majority of these cases, and as such arthroplasty, in the case of diarthrodial joints, and surgical-induced ankylosis for vertebral fusion are the most common interventions employed for these unsalvageable joints. Spine: Low Back and Neck Pain, in United States Bone and Joint Decade: The Burden of Musculoskeletal Diseases in the United States. 2008, American Academy of Orthopaedic Surgeons: Rosemont, Ill.
Joint prostheses have an obvious advantage over fusion due to at least a partially preserved functionality, but both clinical treatments are plagued with exorbitant costs, native tissue morbidity, and extensive rehab/recovery, and they may lead to unforeseen complications and traumatic revision surgery. This outcome present needs for improved, economical treatment modalities. especially in regard to the disc. Khan S N, and Stirling A J. Controversial topics in surgery: degenerative disc disease: disc replacement. Against. Ann R Coll Surg Engl 2007; 89(1): p. 6-11. Wilson-MacDonald J, and Boeree N. Controversial topics in surgery: degenerative disc disease: disc replacement. For. Ann R Coll Surg Engl 2007; 89(1): p. 6-11. Although the pains and costs associated with the treatment of diarthrodial joints such as hips and knees is evident through the long road of pain management leading to arthoplasty. Hunter D J, and Lo G H. The management of osteoarthritis: an overview and call to appropriate conservative treatment. Rheum Dis Clin N Am 2008; 34: p. 689-712. Surgeons, scientists, and engineers have made many attempts to restore functional, biomechanically stable cartilage within these articulating joints through grafting procedures with little to no repeatable success. Revell C M, and Athanasiou K A. Success rates and immunologic responses of autogenic, allogenic, and xenogenic treatments to repair articular cartilage defects. Tissue Eng Part B Rev 2009; 15(1): p. 1-15.
Use of resorbable, regenerative synthetic biomaterial composites within joints is an attractive possibility but, has traditionally performed less effectively than grafting and results have been highly variable. Although initial success is common, osteochondral grafting (allogenic tissue graft) commonly fails long-term. These inconsistent and failed attempts suggest the underlying causes of cartilage degeneration are not being circumvented by these clinical practices and researched treatments. Accompanying joint degeneration, and manifesting prior to complete cartilage failure, is a change in the underlying subchondral and cancellous bone. Most notably is advancing calcified cartilage (tidemark) early in the disease, and osteophyte formation around invading vessels in the advanced state. Goldring S R. The role of bone in osteoarthritis pathogenesis. Rheum Dis Clin North Am 2008; 34(3): p. 561-71. Accompanying abnormal subchondral plate thickness, adjacent trabecular bone mineral density increases with alterations in architecture, resulting in brittleness. Id. Within the knee and hip, bone may become necrotic in severe cases, eventually collapsing under physiological loading, resulting in destruction of the articular surface. Bancroft L W, Peterson J J, and Kransdorf M J. Cysts, geodes, and erosions. Radiol Clin North Am 2004; 42(1): p. 73-87. Carrino J A, Blum J, Parellada J A, Schweitzer M E, and Morrison W B. MRI of bone marrow edema-like signal in the pathogenesis of subchondral cysts. Osteoarthritis Cartilage 2006; 14(10): p. 1081-5. In the spine, the vertebral cortex thickens adjacent to the disc, causing occlusion of vascular supplied diffusion pathways which link the disc to the surrounding vertebral bodies. Adams M A, and Roughley P J. What is intervertebral disc degeneration, and what causes it? Spine 2006; 31(18): p. 2151-61.
It is reasonable to believe that this loss of a nutrient pathway across the vertebral cortex and endplate to the disc or across subchondral bone in articulating joints leads to the cellular apoptosis and tissue turnover associated with early stages of joint degenerative; later, osteophytes and vessels invade, bringing nerve ending and the associated pains. A technique to restore this nutrient pathway solves a long standing need in the medical field of subchondral bone associated with diarthrodial and endplates and vertebral cortex and endplate associated with spinal discs.